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Command line tool and ruby interface to optimize (lossless compress, optionally lossy) jpeg, png, gif and svg images using external utilities:

Based on

Documentation for latest gem version and master branch.

A test application with latest image_optim and image_optim_pack is available on render:

Gem installation

gem install image_optim

You may also want to install image_optim_pack (see Binaries pack).

gem install image_optim_pack


Add to your Gemfile:

gem 'image_optim'

With image_optim_pack:

gem 'image_optim'
gem 'image_optim_pack'

With version:

gem 'image_optim', '~> 0.31'

If you want to check latest changes:

gem 'image_optim', :git => 'git://'


This gem is also be available as docker image containing most binaries:

docker run --rm --version # image_optim version
docker run --rm --info # image_optim info including bin versions
docker run --rm -v "$PWD":/here -w /here image-in-this-folder.jpg

See image_optim_pack repository for Dockerfile and instructions.

Binaries location

Simplest way for image_optim to locate binaries is to install them in common location present in PATH (see Binaries installation).

If you cannot install to common location, then install to custom one and add it to PATH.

Specify custom bin location using XXX_BIN environment variable (JPEGOPTIM_BIN, OPTIPNG_BIN, …).

Besides permanently setting environment variables in ~/.profile, ~/.bash_profile, ~/.bashrc, ~/.zshrc, … they can be set:

  • before command:

PATH="/custom/location:$PATH" image_optim *.jpg

for example:

PATH="/Applications/$PATH" image_optim *.jpg

  • inside script:

ENV['PATH'] = "/custom/location:#{ENV['PATH']}"; ImageOptim.optimize_images([…])

for example:

ENV['PATH'] = "/Applications/{ENV['PATH']}"; ImageOptim.optimize_images([…])

Binaries installation

Binaries pack

Easiest way to get latest versions of most binaries for image_optim for Linux and Mac OS X is by installing image_optim_pack gem.

Check installation instructions in Gem installation section.

Pack doesn't include pngout and svgo binaries, their installation instructions are provided below.

Linux - Debian/Ubuntu

sudo apt-get install -y advancecomp gifsicle jhead jpegoptim libjpeg-progs optipng pngcrush pngquant

If you get an old version of pngquant, please check how to install up-to-date version or compile from source at

Linux - RHEL/Fedora/Centos

sudo yum install -y advancecomp gifsicle jhead libjpeg optipng pngquant

You may also need to install libjpeg-turbo-utils instead of libjpeg:

sudo yum install -y libjpeg-turbo-utils

You will also need to install jpegoptim and pngcrush from source:


Replace X.Y.Z with latest version number from

cd /tmp
tar zxf jpegoptim-$JPEGOPTIM_VERSION.tar.gz
./configure && make && make install


Replace X.Y.Z with latest version number from

cd /tmp
tar zxf pngcrush-$PNGCRUSH_VERSION.tar.gz
make && cp -f pngcrush /usr/local/bin

OS X: Macports

sudo port install advancecomp gifsicle jhead jpegoptim jpeg optipng pngcrush pngquant

OS X: Brew

brew install advancecomp gifsicle jhead jpegoptim jpeg optipng oxipng pngcrush pngquant jonof/kenutils/pngout

oxipng installation (optional)

Unless it is available in your chosen package manager, can be installed using cargo:

cargo install oxipng

pngout installation (optional)

If you installed the dependencies via brew, pngout should be installed already. Otherwise, you can install pngout by downloading and installing the binary versions.

Note: pngout is free to use even in commercial soft, but you can not redistribute, repackage or reuse it without consent and agreement of creator. license

svgo installation (optional)

svgo is available from NPM.

npm install -g svgo

If you prefer to install svgo to your project directory, use one of the following commands instead:

npm install svgo

yarn add svgo

When installing svgo to the project directory, you must add the following to your environment:


jpeg-recompress installation (optional)

Download and install the jpeg-recompress binary from the JPEG-Archive Releases page, or follow the instructions to build from source.


From shell

image_optim *.{jpg,png,gif,svg}

image_optim -r .

image_optim -h

From ruby

Initialize optimizer (or you can call optimization methods directly on ImageOptim):

image_optim =

image_optim = => false)

image_optim = => 20)

Optimize image getting temp path:


Optimize image in place:


Optimize image data:


Multiple images:

image_optim.optimize_images(Dir['*.png']) do |unoptimized, optimized|
  if optimized
    puts "#{unoptimized} => #{optimized}"



From rails

Rails image assets optimization is extracted into image_optim_rails gem.


Configuration in YAML format will be read and prepended to options from two paths:

  • $XDG_CONFIG_HOME/image_optim.yml (by default ~/.config/image_optim.yml)
  • .image_optim.yml in current working directory

Paths can be changed using :config_paths option and --config-paths argument.

Example configuration:

nice: 20
pngout: false # disable
  level: 5

Temporary directory

image_optim uses standard ruby library for creating temporary files. Temporary directory can be changed using one of TMPDIR, TMP or TEMP environment variables.


  • :nice — Nice level, priority of all used tools with higher value meaning lower priority, in range -20..19, negative values can be set only if run by root user (defaults to 10)
  • :threads — Number of threads or disable (defaults to number of processors)
  • :verbose — Verbose output (defaults to false)
  • :pack — Require image_optim_pack or disable it, by default image_optim_pack will be used if available, will turn on :skip-missing-workers unless explicitly disabled (defaults to nil)
  • :skip_missing_workers — Skip workers with missing or problematic binaries (defaults to false)
  • :allow_lossy — Allow lossy workers and optimizations (defaults to false)
  • :cache_dir — Configure cache directory
  • :cache_worker_digests - Also cache worker digests along with original file digest and worker options: updating workers invalidates cache
  • :timeout — Maximum time in seconds to spend on one image, note multithreading and cache (defaults to unlimited)

Worker can be disabled by passing false instead of options hash or by setting option :disable to true.


  • :level — Compression level: 0 - don't compress, 1 - fast, 2 - normal, 3 - extra, 4 - extreme (defaults to 4)


  • :interlace — Interlace: true - interlace on, false - interlace off, nil - as is in original image (defaults to running two instances, one with interlace off and one with on)
  • :level — Compression level: 1 - light and fast, 2 - normal, 3 - heavy (slower) (defaults to 3)
  • :careful — Avoid bugs with some software (defaults to false)


Worker has no options


  • :allow_lossy — Allow limiting maximum quality (defaults to false)
  • :strip — List of markers to strip: :com, :exif, :iptc, :icc, :xmp, :none or :all (defaults to :all)
  • :max_quality — Maximum image quality factor 0..100, ignored in default/lossless mode (defaults to 100)


  • :allow_lossy — Allow worker, it is always lossy (defaults to false)
  • :quality — JPEG quality preset: 0 - low, 1 - medium, 2 - high, 3 - veryhigh (defaults to 3)
  • :method — Comparison Metric: mpe - Mean pixel error, ssim - Structural similarity, ms-ssim - Multi-scale structural similarity (slow!), smallfry - Linear-weighted BBCQ-like (may be patented) (defaults to ssim)


  • :copy_chunks — Copy all chunks (defaults to false)
  • :progressive — Create progressive JPEG file (defaults to true)
  • :jpegrescan — Use jpegtran through jpegrescan, ignore progressive option (defaults to true)


  • :level — Optimization level preset: 0 is least, 7 is best (defaults to 6)
  • :interlace — Interlace: true - interlace on, false - interlace off, nil - as is in original image (defaults to false)
  • :strip — Remove all auxiliary chunks (defaults to true)


  • :level — Optimization level preset: 0 is least, 6 is best (defaults to 3)
  • :interlace — Interlace: true - interlace on, false - interlace off, nil - as is in original image (defaults to false)
  • :strip — Remove all auxiliary chunks (defaults to true)


  • :chunks — List of chunks to remove or :alla - all except tRNS/transparency or :allb - all except tRNS and gAMA/gamma (defaults to :alla)
  • :fix — Fix otherwise fatal conditions such as bad CRCs (defaults to false)
  • :brute — Brute force try all methods, very time-consuming and generally not worthwhile (defaults to false)
  • :blacken — Blacken fully transparent pixels (defaults to true)


  • :copy_chunks — Copy optional chunks (defaults to false)
  • :strategy — Strategy: 0 - xtreme, 1 - intense, 2 - longest Match, 3 - huffman Only, 4 - uncompressed (defaults to 0)


  • :allow_lossy — Allow quality option (defaults to false)
  • :max_colors — Maximum number of colors to use (defaults to 256)
  • :quality — min..max - don't save below min, use less colors below max (both in range 0..100; in yaml - !ruby/range 0..100), ignored in default/lossless mode (defaults to 100..100, 0..100 in lossy mode)
  • :speed — speed/quality trade-off: 1 - slow, 3 - default, 11 - fast & rough (defaults to 3)


  • :disable_plugins — List of plugins to disable (defaults to [])
  • :enable_plugins — List of plugins to enable (defaults to [])


List of contributors to image_optim.

If you would like to contribute - that is great and you are very welcome. Please check few notes in file CONTRIBUTING.markdown.


In separate file CHANGELOG.markdown.

Copyright (c) 2012-2023 Ivan Kuchin. See LICENSE.txt for details.